The invention is directed to a method of manufacturing a color television focusing mask for TV tubes which include an evacuated envelope, an electrode system to generate at least two electron beams, a display screen covered with a large number of regions luminescing in different colors, and color selection means arranged a short distance in front of the display screen for assigning each electron beam to luminescent regions of one color. The color selection means usually used is in the form of a perforated plate, known as a shadow mask, which is arranged at a short distance in front of or before the display screen. A drawback of such a shadow mask is that a large part, for example 80-85%, of the electrons are intercepted, which imposes restrictions upon the maximum achievable brightness of the displayed picture. When the shadow mask, however, is replaced by a focusing mask, such as is known in the industry, many more electrons are on target and the brightness of the picture is increased substantially, or in the alternative reduced voltages may be utilized to maintain the brightness achieved with conventional shadow masks.
Focus masks, such as shown in U.S. Pat. Nos. 4,066,923; 4,160,311; 4,164,059; and 4,222,159 are known in the prior art and may consist of a sheet or set of interconnected conducting strips which form one system of lens electrodes connected mechanically by means of insulating material to an apertured plate or second set of conducting strips which form another set of lens electrodes. As shown by the various manufacturing methods employed in said aforementioned patents, one of the problems encountered in manufacturing such focus masks was that of precisely locating the strips or columns of insulation with respect to the apertures within the mask, and then positioning another conductor on top of the strips or columns so as to be in desired orientation with respect to such apertures. In U.S. Pat. No. 4,066,923, an etched grid plate and etched apertured plate are first coated with layers of gold and then pressed against an insulating foil which is coated on both sides with layers of copper to effect a diffusion bond between the layers of copper and gold. The uncovered parts of the copper layers are then etched away to form the apertures through the mask.
In the method set forth in U.S. Pat. No. 4,160,311, a metal plate is first etched so as to provide a relief pattern having a plurality of ridges separated by strip-shaped regions having a small thickness. A suitable insulator in the form of glass powder may then be applied to the upper faces of the ridges by utilizing an electrophoresis bath and protecting those parts of the ridged plate not to be covered with the glass powder by use of a suitable protector material. The protected material is then removed and the glass powder is converted into a solid glass by heating, and a ridged plate is obtained which has a relief and a layer of solid glass on the ridges. Such plate may then be placed against an apertured plate or against another plate having a similar relief and the plates secured together by heating. The strip-shaped regions are then removed by etching and a grid shaped focus mask having a pair of apertured plates separated by insulating glass strips is provided.
In the process disclosed by U.S. Pat. No. 4,164,059, a color selection means or focusing mask is formed by first coating two sides of the polyimide foil with layers of metal which are then provided with a photoresist material and exposed to develop a pattern of parallel metal strips on each side of the polyimide foil, with the parallel strips on one side of the foil extending 90.degree. to the parallel strips on the opposite side. The portions of the foil disposed between the strip conductors are then etched away without attacking the conductors such that only blocks of the original foil remain in areas where the conductors on one side cross the conductors on the other side.
U.S. Pat. No. 4,222,159 sets forth various methods of producing color selection means or focus masks including a continuous method utilizing a roll of polyimide foil covered with a metallic film and a roll of metal plate material having apertures formed therein. The roll of polyimide foil which is covered with a metal film is cut into a plurality of strips to form electrodes, and the roll of metal plate having apertures formed therein is continuously fed under a pressure roll which presses the electrode strips between the apertures of the metal plate, which is covered with a polyamide solution. Strips of lens electrodes are then guided through a high frequency furnace which converts the polyamide into polyimide and the strips are cut into plates or focusing masks wherein the metal plate is insulated from the electrode strips by the polyimide foil.
According to U.S. Pat. No. 4,107,569, the relevant electrodes of the focus mask are kept at a defined distance from each other by grains of an electrically insulating material such as Al.sub.2 O.sub.3 present between the facing surfaces of the electrodes, which grains are sunk on two sides in layers of adhesive material present on the two surfaces of the electrodes. In the focus mask set forth in U.S. Pat. No. 4,121,131, apertures are first etched into a pair of opposed iron plates and glass fibers consisting of a hard glass core and a soft glass jacket are positioned on the plates between the rows of the apertures and heated in a furnace to the softening temperature of the glass jacket. Finally, as shown in U.S. Pat. No. 2,650,900, a complex method is set forth for producing a metal mesh screen wherein a sheet of thermoplastic material is impressed with an exact copy of the original groove system which is coated with a thin film of suitable metal. The coated surface is then lightly lapped until the metal film is removed from portions of the surface lying between the grooves, leaving such portions clean and nonconductive, whereas a continuous conductive film or layer remains within the grooves. The matrix is then placed in an electro-deposition bath and a further metal deposit is applied to the metal already in the groove, which reinforces the otherwise mechanically weak structure of the previously deposited metal film. The sheet of thermoplastic material is then heated and the completed mesh removed from the grooves.
The present invention materially simplifies the manufacture of focus masks by easily and efficiently locating strips or columns of insulating material with respect to the holes or apertures formed in the focus mask and then easily and simply applying another conductor or plate on top of the strips or columns.